The present invention relates to the industrial field of a diagnosis by radiation images in medical care. In particular, it relates to a radiation image detector for obtaining radiation images used for a purpose of diagnoses.
As a method to obtain a radiation image, there has been used the so-called screen film system (SF system) in which a fluorescent screen and a film for radiography are combined. In this SF system, when radiation such as an X-ray transmitted through a subject enters a fluorescent screen, a phosphor contained in the fluorescent screen absorbs energy of the radiation to emit fluorescence. By this luminescence, a film for radiography that is superposed on the fluorescent screen to be close thereto is exposed, and a radiation image is formed on the film for radiography.
On the SF system, however, it is necessary to radiograph after making the spectral sensitivity region of the film for radiography to agree with that of the fluorescent screen. Further, the film for radiography needs to be subjected to chemical development and fixing, thus, it takes time to obtain radiation images and a developing solution and a fixing bath thus used are changed into a waste liquor, which is not preferable from the environmental view point.
Since an image in the SF system is an analog image, an operation to transfer image signals of the radiation images obtained by the SF system into digital signals is required to carry out remote diagnosis that utilizes a digital network system.
In the recent radiation image radiographing system, therefore, there is available a system to obtain radiation images by taking out digital and electric signals of radiation images, such as a computed radiography (CR) and a flat panel type radiation detector (FPD) serving as a digital type X-ray diagnosis apparatus in place of the SF system. The system of this kind does not use a radiation film which is used by the SF system, and therefore, there is no complicated process such as a developing process, and radiation images can be drawn quickly on a screen of an image display device, for example, on a screen of a cathode ray tube or a liquid crystal display panel.
In the field of the medical image diagnosis, a digital radiation image detecting means such as a computed tomograph (CT) and a nuclear magnetic resonance imaging (MRI) are commonly used recently, and thereby, the remote diagnosis has been made simple by using a network for images together with the images of the digital radiation image detecting means.
Further, the radiation image radiographing system used in the medical care site can be divided into a xe2x80x9cfloor typexe2x80x9d and a xe2x80x9ccassette typexe2x80x9d. The xe2x80x9cfloor typexe2x80x9d is one to be used mainly for radiographing of a chest and an abdomen, and it is one wherein a radiation image detector and its peripheral equipment are integrated solidly to be used for radiographing on condition that the xe2x80x9cfloor typexe2x80x9d is constantly installed in a radiographing room. In this case, a patient needs to visit the radiographing room by itself when the patient is radiographed for radiation images.
Regarding the xe2x80x9ccassette typexe2x80x9d, on the other hand, in the case of the SF system, for example, a flat container that is called the cassette in which a fluorescent screen and a radiation film are housed is brought, for radiographing for radiation images, to a bed of a patient who is in a critical state and cannot move at all. Namely, in the xe2x80x9ccassette typexe2x80x9d, a portable radiation emitting apparatus and a cassette are conveyed to a bed of a patient, and the patient can be radiographed while lying on the bed. In the case of chest-radiographing, for example, it is said that the radiographing using a cassette occupies 50% of the total chest-radiographing.
Incidentally, though CR representing a digital radiation image detector can be used as a radiation image detector of a cassette type, in the same way as in the SF system, it is expensive and it cannot offer image quality which is the same as that in the SF system. FPD, on the other hand, can offer image quality that is equal to or better than that in the CR, but it is expensive in the same way as in the SF system, and it is difficult to realize a light radiation image detector of a cassette type.
In the invention, therefore, there is to be provided a radiation image detector which is inexpensive and light in weight and can make a digital radiation image with high image quality to be obtained.
A radiation image detector related to the invention is provided with a first layer that conducts light emission based on intensity of radiation entered, a second layer that converts light emitted from the first layer into electric energy, a third layer that outputs signals based on accumulation of the electric energy obtained by the second layer and on the accumulated electric energy, and a fourth layer that holds the first layer, the second layer and the third layer, and image signals of the radiation entered are outputted based on the signals outputted from the third layer, and the fourth layer is formed with resin.
In the present invention, the first layer, the second layer and the third layer are formed on the fourth layer that is made of resin. The first layer is formed by using, for example, cesium iodide (CsI:Tl) or gadolinium oxysulfide (Gd2O2S:Tb), and light emission corresponding to intensity of the radiation entered is conducted. The second layer is formed by using an organic compound capable of conducting photoelectric conversion, for example, conductive polymer containing fullerene or carbon nanotube, and light outputted from the first layer is converted into electric energy. The third layer is formed by using an organic semiconductor or an element of a layer upon layer structure of divided silicone, and it outputs signals based on accumulation of the electric energy obtained by the second layer and on the accumulated electric energy, thus, image signals of the radiation image are outputted based on the signals outputted from the third layer.
Further, the radiation image is made to be of a portable structure, and a power supply means structured with a sheet-shaped battery, for example, is provided, and power necessary to drive the radiation image detector is supplied from the power supply means. Further, a memory means that stores image signals is provided.